A wide variety of doors have been designed for use in large industrial doorways. Such doorways are typically large enough to admit vehicles such as trucks. Conventional factory doors, however, are typically cumbersome and difficult to open and close rapidly. This led to the development of a variety of door designs providing doors which could be rapidly opened to admit a vehicle, or pushed open by a vehicle passing through.
Certain recent industrial doors utilize a series of flexible strips which hang down from the top of a doorway. The following patents and patent publications are illustrative of such designs: Schaefer U.S. Pat. No. 4,388,961 issued June 21, 1983, Schenker U.S. Pat. No. 4,310,044 issued Jan. 12, 1982, Schenker U.S. Pat. No. 4,382,461 issued May 10, 1983, Brabant U.S. Pat. No. 4,449,270 issued May 22, 1984, Catan U.S. Pat. No. 4,289,190 issued Sept. 15, 1981, Simon U.S. Pat. No. 4,335,777 issued June 22, 1982, Schenker et al. U.S. Pat. No. 4,186,790 issued Feb. 5, 1980, Sills U.K. Patent Application No. 2,080,379 published Feb. 3, 1982, and Klein Patentschrift DE No. 3,048,763, published June 9, 1983. Such doors are typically designed to open and close as rapidly as possible, to minimize damage in the event a vehicle should collide with the door, and to prevent unwanted loss or gain of heat through the doorway as much as possible.
Other types of flexible doors are also known. For example, Tohma U.S. Pat. No. 4,027,715 issued June 7, 1977, is illustrative of a door comprising a series of plate-like unit blocks or segments. Hinged flexible industrial doors are also known. See, for example, McGuire U.S. Pat. No. 3,750,739 issued Aug. 7, 1973, and Mackie British Patent Specifications No. 1,370,611 published Oct. 16, 1974 and No. 1,410,461 published Oct. 15, 1975. None of these other flexible doors are particularly well adapted for covering the entrance to a large industrial refrigerator or freezer, wherein both ease of access and good insulating properties are needed.
This invention provides a folding door which utilizes a specially designed curtain. One common type of curtain comprises a sheet, piece of fabric, or screen suspended on an overhead track by a series of hangers movably mounted in that track. See, for example, Sandall British Patent No. 1,554,159 published Oct. 17, 1979. Overlapping flexible sheets have also been used to provide a flexible wall, as illustrated by Johnson U.S. Pat. No. 3,561,518 issued Feb. 9, 1971. Ordinary curtains are not generally well adapted for use in industrial doors, since such curtains are generally cumbersome and lack thermal insulating properties.
The present invention provides an improved industrial door which is both highly insulated and capable of being opened and closed rapidly. The folding door according to the invention represents a distinct improvement over the hanging strip-type doors, such as the door of German Patent No. 3,048,763 noted above.